Here is what I mean by original. When I collected my American Elm, it was simply a stump, and during the spring it produced quite a lot of growth. I removed most of this growth and the remaining shoots all grew out to about 2-3 feet and had a set of alternating leaves and no side branches. As I've cut this tree back, some of the original set of leaves have remained alongside the new growth that the tree has produced. Now, the initial set of leaves have begun to turn yellow/brown and die off. The rest of the tree is fine though.

Is this a natural process? I know some trees can be partially deciduous, and drop leaves during the drop season. Could this be the case, or is there something else to worry about?

I think it's part of the natural process, I won't worry about it. They have outlived their usefulness and it's time for them to go. If it dried out they'd be the first to go too. I assume this is the floridana subspecies of American elm, I have one also. Does it go through a total leaf drop and dromancy during a winter period for you?

I think it's part of the natural process, I won't worry about it. They have outlived their usefulness and it's time for them to go. If it dried out they'd be the first to go too. I assume this is the floridana subspecies of American elm, I have one also. Does it go through a total leaf drop and dromancy during a winter period for you?

Yes, Florida subspecies, and it does go through a full leaf drop and dormancy.